Try to think what should be changed in the near future (5 or 10 years) to make that better world

Design something that can help making this improvement

Introduce the sustainable aspects of your design in a presentation. Point out how it influences the Sustainable Footprint of the users.

Subjects full of possibilities:

Waste can produce energy when it is burnt, but a big part of it can be used as a resource for producing new products. Nearly every kind of waste can be recycled. In nature everything goes in cycles. A sustainable society can only be possible when materials are being recycled all the time and no real waste is produced.

Many machines should possible be working on much less energy.

New ways of creating sustainable energy could be on a much smaller scale.

Transport of goods will decrease if the production is local.

Violent conflicts are bad for sustainability If humankind would learn to solve conflicts without violence, the footprint of mankind would be much smaller.

On this site you can find some information to inspire you:
some futuristic buildings are already being realised like in Chicago, but exisitng buildings can be made ready for a green future like in Toronto.
In the news pages you can find other ideas.
How the world will look like according to somebody whe works in this field you can read in Earth Day 2058